So who really is this Obama who can reduce knees and brains to jelly, whose books are read with reverence by normally pungent critics, and who, we are told, is the new JFK? I travelled to his home city, Chicago, to see if I could find out...

He has written his own sunlit, often rather purple account of his life, with just enough revelation to persuade us that we know all we need to know. The book, Dreams From My Father, is a much-praised bestseller (though I suspect many of those who praised it didn't stick it out to the end). It contains a confession of drug-taking, carefully limited - marijuana and cocaine but no heroin. It is sometimes moving but often exasperating.

Obama has black skin and was deserted by his father at the age of two. His mother seems to have been a little vague about life. But his devoted grandparents, especially his hard-working grandmother, saw to it that young Barry, as he was then known, got a private education. This lifted him way above the miseries of most black Americans. Under the circumstances, there may be a little too much in the memoirs about how tough it was to be black.

Crucially, the story stops just where things get interesting - when Obama first entered politics in Chicago, that mythical city of gangsterism, corruption and one party-state politics. He did this as an Illinois State Senator, representing a largely black and liberal section of Capone's hometown.

Now, Obama has the devil's luck, which among other things means he has a boyish smile that disarms suspicion or hostility at 50 paces. But he is no child, and no innocent. Despite a childhood in Hawaii and Indonesia, Obama knows Chicago well - and from underneath, too.

He threw over a good corporate job in New York to toil in the dismal South Side as a "community organiser", getting up campaigns about asbestos in council flats but also getting to know this place's grimy, snaggled web of power - churches, property developers, professional politicians, fixers and money men.

He also revealed that he was the sort of person who goes into a revolving door behind you and then comes out of it in front of you. And, of course, he is a lawyer who knows the rules all too well.

As one veteran of Chicago politics who very much did not want to be named said to me: "Thank God for Louisiana - their politics are even dirtier than ours."

He clearly remembered Obama's first steps on his political career. This involved merciless cunning.

Somehow, all of Obama's challengers made a mess of their nomination papers. They were all disqualified. Only Obama's papers, miraculously, were perfect. So he won the Democratic nomination, which in this part of the world means he won the seat.

The insider recalled: "I thought he was a very talented young man. He was smart, he was willing, he was principled and he worked hard.

"He went to Springfield [the Illinois state capital] and did not become part of the more tawdry aspects of the culture down there - alcohol and women.

But Obama quickly got another reputation. "He was always in the bathroom for the really tough votes. It was not courageous."

The source explained this simply. Barack Obama knew even then that he could one day live in the White House.

"I think he understood long ago that the future was limitless for him. He made decisions in his very early political life that would enable him to be a candidate who would have very broad appeal."

These not-very-helpful remarks come from a black member of Obama's own party. What about his opponents?

One who remembers him well is Illinois State Senator Bill Brady, a white conservative Republican. The two arrived in Springfield together. In the evenings, they would gather for a friendly card game.

"There was a group of us who used to play poker," said Brady. "He was a conservative player. I said to him, 'If you were half as conservative with the taxpayers' dollars as you are at the poker table, the people of Illinois would be a lot better off.' "We were mostly playing for beers and giggles but he took it as seriously as anybody. I recall him never getting too far down."

Brady also recalled a tendency to have it both ways and to dodge difficult votes that might hurt him later in life: "I saw great ambition in him, no question. He had an agenda."

As for his voting performance, Brady agreed Obama liked sitting on the fence. He is recalled for taking full advantage of an Illinois rule that lets you vote "present" if you don't want to commit yourself.

Brady recalled: "I learned very quickly that the 'present' vote, where the button you press is very appropriately coloured yellow, is the chicken's way out."

But that did not mean Obama lacked convictions. On the contrary, when it suited him he would vote as far Left as he could. "No one was further Left. He would do things that were unrealistic to prove he was Left.

"He was not far Left for political benefit but because he was a true believer.

"But these would be on broad-brush issues - unlike, say, detailed abortion laws - where it was unlikely to be held against him. I have never heard anyone say so little about detailed policies . . . He has moderated his tones, but I don't think he has moderated his beliefs," said Brady.

Both these politicians also mentioned Obama's money problems. These were big. Money for TV campaigns is the original sin of US politics. No one can get anywhere without it. And, as recounted in a refreshingly ungushing biography by David Mendell, Obama was seriously short of cash. When he went to the Democratic Party convention in Los Angeles in 2000 he couldn't hire a car to get around because his credit card was maxed out.

About that time, his amazing luck seemed to fail him and an attempt to run for the US House of Representatives collapsed, largely for lack of funds. It was, it turned out, a good thing. Four years later he was free to run for the US Senate, a far better route to the prize he seeks. When that came around, good fortune swept him to Capitol Hill so sweetly that he hardly had to open his mouth or spend any of the millions of dollars he had finally managed to raise.

It was almost like the film The Omen. Anybody who got in his way just melted away or met a nasty end. But this time nobody could possibly blame him, though the mysterious figure of his feared spin-doctor David Axelrod lurks in the background here, and some suspect his hand in at least some of Obama's luck.

The first slice of good fortune was that the seat was empty - the incumbent suddenly retired, citing "family issues". The former Democratic holder of the seat, prominent black politician Carol Moseley Braun, could have had it for the asking - and Obama would not have dared challenge her - but she ruled herself out. That still left a couple of major Democratic challengers. But Obama unexpectedly won union support and wiped out one of them. The second, Blair Hull, was a tougher proposition until details of his divorce papers were unsealed, revealing his wife's accusations of abuse, which virtually destroyed him.

Obama won the Democratic nomination.

To win election to the Senate, Obama would have had a major battle against Republican Jack Ryan. But then Ryan's divorce papers were also unsealed, revealing that his wife Jeri - an actress famous for her tight costumes in Star Trek: Voyager - had accused him of pressuring her to have sex in public in kinky clubs.

Ryan denied it, but that was the end of him.

The Republicans pretty much gave up the struggle at this stage, picking a candidate who had no connections with Illinois. Obama couldn't lose.

By this time, he had learned how to raise money, persuading Hyatt hotel magnate Penny Pritzker he was worth backing, a boost that immediately brought in many more wealthy liberals flapping their chequebooks at the charming young man.

But he had also got mixed up with the Syrian-American property magnate and alleged "slumlord" Tony Rezko, who, as I write, languishes a few hundred yards from me in a Chicago jail, having had his bail revoked on serious fraud charges.

The Rezkos had known Obama since 1990 and even held a fundraising party for him at their mansion in the wealthy suburb of Wilmette.

Obama bought a new home, a big Edwardian-era detached house in fashionable Kenwood, soon after he won his Senate seat in 2004. The former owner apparently wasn't willing to sell the house without a large chunk of land next to it, which Obama seemingly couldn't afford. The house cost $1.65 million and the land $625,000. Rezko's wife Rita bought the vacant land. Six months later, she sold Obama a slice of it for $104,500 so that he could extend his garden.

By that time, Tony Rezko was already under federal investigation. Worse, letters have since come to light in which Obama lobbied city officials on Rezko's behalf.

The Clintons don't dare make too much of this Obama skeleton because people will remind them of their own odd dealings with property companies and commodity traders.

But one Chicago Democratic professional told me: "I cannot believe Obama got so beholden to that man just to buy a big house."

Obama now says he agrees, describing the transaction as "boneheaded". But it cannot now be undone....